From: Marc-André Lureau <[email protected]> A malicious usbredir peer can send an ep_info message resetting max_packet_size to 0 after bulk receiving has started. This causes: - infinite loop in usbredir_buffered_bulk_packet() where the splitting loop increments by max_packet_size (0) - SIGFPE in usbredir_buffered_bulk_in_complete_ftdi() from modulo by 0 - SIGFPE in usbredir_handle_buffered_bulk_in_data() from division by 0 when computing bytes_per_transfer
Fix by stopping and disabling bulk receiving in usbredir_ep_info() when max_packet_size is set to 0. Add post-load check, and assert() for the invariant. Fixes: CVE-2026-63319 Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3995 Reported-by: Tristan @TristanInSec Signed-off-by: Marc-André Lureau <[email protected]> --- hw/usb/redirect.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/hw/usb/redirect.c b/hw/usb/redirect.c index 284bcbdb34d..dfd9e8bb50c 100644 --- a/hw/usb/redirect.c +++ b/hw/usb/redirect.c @@ -690,6 +690,7 @@ static void usbredir_buffered_bulk_in_complete_ftdi(USBRedirDevice *dev, struct buf_packet *bulkp; int count; + assert(maxp != 0); while ((bulkp = QTAILQ_FIRST(&dev->endpoint[EP2I(ep)].bufpq)) && p->actual_length < p->iov.size && p->status == USB_RET_SUCCESS) { if (bulkp->len < 2) { @@ -739,6 +740,7 @@ static void usbredir_handle_buffered_bulk_in_data(USBRedirDevice *dev, .stream_id = 0, .no_transfers = 5, }; + assert(dev->endpoint[EP2I(ep)].max_packet_size != 0); /* Round bytes_per_transfer up to a multiple of max_packet_size */ bpt = 512 + dev->endpoint[EP2I(ep)].max_packet_size - 1; bpt /= dev->endpoint[EP2I(ep)].max_packet_size; @@ -793,6 +795,7 @@ static void usbredir_handle_bulk_data(USBRedirDevice *dev, USBPacket *p, } if (dev->endpoint[EP2I(ep)].bulk_receiving_enabled) { + assert(maxp != 0); if (size != 0 && (size % maxp) == 0) { usbredir_handle_buffered_bulk_in_data(dev, p, ep); return; @@ -1796,6 +1799,17 @@ static void usbredir_ep_info(void *priv, if (usbredirparser_peer_has_cap(dev->parser, usb_redir_cap_ep_info_max_packet_size)) { dev->endpoint[i].max_packet_size = ep_info->max_packet_size[i]; + if (ep_info->max_packet_size[i] == 0 && + dev->endpoint[i].bulk_receiving_enabled) { + USBPacket *p = dev->endpoint[i].pending_async_packet; + usbredir_stop_bulk_receiving(dev, I2EP(i)); + dev->endpoint[i].bulk_receiving_enabled = 0; + if (p != NULL) { + dev->endpoint[i].pending_async_packet = NULL; + p->status = USB_RET_IOERROR; + usb_packet_complete(&dev->dev, p); + } + } } #if USBREDIR_VERSION >= 0x000700 if (usbredirparser_peer_has_cap(dev->parser, @@ -2156,6 +2170,7 @@ static void usbredir_buffered_bulk_packet(void *priv, uint64_t id, } /* Data must be in maxp chunks for buffered_bulk_add_*_data_to_packet */ + assert(dev->endpoint[EP2I(ep)].max_packet_size != 0); len = dev->endpoint[EP2I(ep)].max_packet_size; status = usb_redir_success; free_on_destroy = NULL; @@ -2239,6 +2254,15 @@ static int usbredir_post_load(void *priv, int version_id) usbredir_setup_usb_eps(dev); usbredir_check_bulk_receiving(dev); + for (int i = 0; i < MAX_ENDPOINTS; i++) { + if (dev->endpoint[i].bulk_receiving_started && + dev->endpoint[i].max_packet_size == 0) { + error_report("usbredir: endpoint %d has bulk receiving started " + "with zero max_packet_size", i); + return -EINVAL; + } + } + return 0; } -- 2.55.0
